Gas adsorption materials, such as active carbon and zeolite, usually cause second pollution after being used, due to their non-degradability. Here, we prepared a degradable aerogel material based on cellulose nanocrystals (CNCs) and poly vinyl alcohol (PVA) with hierarchical pores and excellent CO2-adsorption performance. The micropores, whose specific area is 442 m2·g−1, are obtained via in-situ growing MIL-100(Fe) on CNCs and concurrently assembling those CNC particles. The obtained aggregation is further introduced into degradable PVA aerogels, who offer mesopores and macropores. Such a degradable material is as light as 0.216 g·cm−3 and can adsorb 0.357 mmol CO2 per gram, which can hopefully be used in preparing light-weight CO2 collectors.